Change is constant, no living fossils?

[mattw]

My question: biological clocks, such as small subunit RNA in ribosomes, and mitochondrial DNA, can measure geological time --and "distance" between related species, because over time they mutate at a predictable rate, right? Then how can we ever know the real genes of ancient organisms? How is DNA conserved somehow in "living fossils"?

Matt

[kotoreru]

One can never 'know' what ancient DNA was like, only make decent guesses. Molecular clocks at the moment are in turmoil for a number of reasons anyway...

[Darby]

Organisms often called "living fossils" are usually well-adapted to some microenvironment that has remained stable over long periods of time, such as horseshow crabs in surf environments, or pelagic sharks, or lots of tiny organisms. But all we know is that the physically resemble their ancestors - how much they may have changed chemically / genetically over time is harder to determine.

[Locus]

Molecular clock based on the genes that do not changet it s spatial structure at the long time of evolution - thouse genes usially appier at the all organisms. Nevertheless, eve at the such genes it is almost impossible to say wich mutation is completly random, and wich not - becouse not only structure of the coded mollecule influenced by the mutation at the coding regions. (regulatory functions, chromatine fold...)
Evidence that molecular clock not very exact - at the different organism different rates of substitution finded!

[mith]

pick bening mutations